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<TITLE>[Chapter 6] 6.5 The if Statement</TITLE>
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<DIV CLASS=sect1>
<h2 CLASS=sect1><A CLASS="TITLE" NAME="JLR2-CH-6-SECT-5">6.5 The if Statement</A></h2>

<P CLASS=para>
<A NAME="CH06.IF"></A><A NAME="CH06.COND2"></A><A NAME="CH06.COND1"></A>An <tt CLASS=literal>if</tt>
statement determines which of two statements is executed, based
on the value of a Boolean expression:


<p>
<img align=middle src="./figs/jlr0609.gif" alt="[Graphic: Figure from the text]" width=450 height=186 border=0>

<P CLASS=para>
In Java, the expression
in parentheses must produce a <tt CLASS=literal>boolean</tt> value.
This is different from C/C++, which allows any type of expression.

<P CLASS=para>
If the expression in parentheses evaluates to <tt CLASS=literal>true</tt>,
the statement after the parentheses is executed. After that statement
has been executed, the statement following the entire <tt CLASS=literal>if</tt>
statement is executed. If the expression between the parentheses
evaluates to <tt CLASS=literal>false</tt>, the next statement to be
executed depends on whether or not the <tt CLASS=literal>if</tt> statement
has an <tt CLASS=literal>else</tt> clause. If there is an <tt CLASS=literal>else</tt>
clause, the statement after the <tt CLASS=literal>else</tt> is executed.
Otherwise, the statement after the entire <tt CLASS=literal>if</tt> statement
is executed.

<P CLASS=para>
When <tt CLASS=literal>if</tt> statements are
nested, each <tt CLASS=literal>else</tt> clause is matched with the
last preceding <tt CLASS=literal>if</tt> statement in the same block
that has not yet been matched with an <tt CLASS=literal>if</tt> statement.

<P CLASS=para>
Here is an example of an <tt CLASS=literal>if</tt> statement:

<DIV CLASS=screen>
<P>
<PRE>
if (j == 4) {
    if (x &gt; 0 ) {
        x *= 7;
    } else {
        x *= -7;
    }
}
return;
</PRE>
</DIV>

<P CLASS=para>
The outer <tt CLASS=literal>if</tt> statement has no <tt CLASS=literal>else</tt>
clause. If <tt CLASS=literal>j</tt> is not 4, the <tt CLASS=literal>return</tt>
statement is executed. Otherwise, the inner <tt CLASS=literal>if</tt>
statement is executed. This <tt CLASS=literal>if</tt> statement does
have an <tt CLASS=literal>else</tt> clause. If <tt CLASS=literal>x</tt>
is greater than zero, the value of <tt CLASS=literal>x</tt> is multiplied
by 7. Otherwise, the value of <tt CLASS=literal>x</tt> is multiplied
by -7. Regardless of the value of <tt CLASS=literal>x</tt>, the
<tt CLASS=literal>return</tt> statement is executed.

<P CLASS=para>
<b>References</b>
<A HREF="ch03_01.htm#JLR2-CH-3-SECT-1.2">Boolean Type</A>;
<I CLASS=emphasis>Expression</I> 4;
<I CLASS=emphasis>Statement</I> 6

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